This invention pertains to the art of control systems and more particularly to a controller for regulating fluid flow in a pressurized fluid system with attention to various time, pressure, and safety parameters.
The invention is particularly applicable to a control for unattended or remote control of any process requiring one or more fluid or gas control valves to be opened or closed at specific times, pressures, or flow specifications. The control software is especially tailored for application to gas and oil wells including a plunger lift device for maximizing production and efficiency by selectively regulating production and shut-in through close supervision of time, pressure, and safety parameters. The production may be controlled by pressure only, time only, or any combination of the two. In addition, a plunger arrival sensor and delay time programming allows for selective operation to further maximize production and efficiency. However, it will be appreciated by those skilled in the art that the invention could be readily adapted for use in other environments as, for example, where similar control devices and systems are employed to control and regulate other types of fluid transmission and communication.
Gas and oil wells typically have varying production characteristics attributable to such factors as well depth, the types and quantity of fluids present in the well, and the natural gas "rock" pressure. Fluid accumulations in the well tubing particularly inhibit the gas production and, accordingly, should be removed. Such fluid accumulations are usually comprised of salt water and oil. Accordingly, dependent upon the particular characteristics of the well, differing well operating techniques are necessary to adapt and to handle these factors and thereby optimize production.
Some oil and gas wells are produced by using the plunger lift method by which a plunger lifts the liquids (e.g., oil, water) out of the well tubing by using the gas pressure in the casing of the well. The standard method of producing such wells is by a time "on" and a time "off" cycle. An "on" period means that a designated time or pressure has been reached and a flow valve is opened which vents the pressure in the well tubing and allows the plunger to rise to the top of the well bringing oil or water ahead of it. After the plunger has arrived at the top of the well, gas is allowed to flow out of the well through the well tubing. An "off" period means that the flow valve is closed, the plunger falls to the bottom of the well tubing and the well sits idle accumulating gas pressure, which will be used to move the plunger during the "on" cycle, and liquids.
Most wells employ a controller system which alternately shuts-in the well for pressure accumulation in the well casing and then opens it to allow the for the expulsion of gas and fluids through a tubing received in the casing. The various forms and types of well controllers that have heretofore been suggested and employed in the industry have met with varying degrees of success. It has been found that the defects present in most prior well controllers are such that the controllers themselves are of limited economic and practical value.
One method of oil and gas production is by means of a simple open/close time cycle controller or variation thereof. An improvement over the simple timer is shown in U.S. Pat. No. 4,150,721 issued to Norwood. The Norwood controller can modify its preset production time cycle by inputs from manually set pressure switches located on the casing, tubing, or sales line and by limit switches which can indicate low flow rate, plunger arrival, or fluid storage full.
U.S. Pat. No. 4,355,365 issued to McCraken is similar to the Norwood controller. The open cycle time may be initiated by a high limit input from a manually set pressure limit switch on the casing. The close cycle time may be initiated from any low or off limit input from the manually set pressure limit switches on the casing, tubing, or sales line or by the switch indicating plunger arrival. The McCraken controller will also extend the open cycle time by the duration of a high limit input or extend the close cycle time by the duration of a low or off limit input to ensure a full time count per cycle.
A problem with previous time cycle production control systems is the failure of the controllers to provide a means for synchronization of several producing wells into a common sales line. This is more desirable with a field of low volume or stripper wells. A producing well with relatively low rock pressure will not be able to discharge its gas into a sales line which has greater pressure. The stronger wells must be shut-in to permit the weaker wells to produce. Timing of the various wells is important as fluid may build and load up the weaker wells. A time cycle controller must be used but must also have pressure limits and conditional inputs for safety. The Norwood and McCraken controllers have the pressure limits and conditional safety inputs but neither are suitable for synchronization for their time cycles are modified by the inputs The McCraken controller extends its time cycle with the inputs and both McCraken and Norwood controllers terminate the open cycle and transfer the close cycle time low limit of off inputs.
It would be desirable to maintain a "constant time" with reference to the open and close cycles. All wells feeding the common sales line may then be assigned an operating period synchronized to within one second from any given time. This permits the individual wells the opportunity to produce at their optimum. The safety and line pressure limits would override an open cycle to close the main production valve only as long as the input condition exists. The time cycle would not be modified and the production valve would reopen for the duration of the open cycle when the line pressure limit or input condition no longer is active. If during the shut in condition of the open cycle, the open cycle time is complete, the close time would be transferred and the well would remain shut in.
Another problem associated with the previous time cycle production control systems is the failure of the controller to be adaptable to changing well conditions due to well aging. Generally, as a well ages, the method of production used when the well was originally tapped, gradually becomes less efficient. It is possible that an initially strong well will become so weak as to necessitate an injection method to achieve an acceptable level of production.
It would be desirable to provide a single controller configurable to a plurality of applications without extensive hardware modification. As a particular well ages, the system program of the controller may be modified to account for the changing conditions when it becomes necessary to do so.
The collection of data representative of the conditions of gas and oil wells typically involves on-site inspection by an operator of the volume of gas and fluids collected for a given time period. A number of collections may be accumulated to form a history against which future data may be evaluated by the operator Because the gas and oil wells are typically spread out over a large area, personnel in charge of maintaining the wells spend much of their time travelling between the sites. Various data collection methods have been proposed which would enable an operator to use an interrogation unit to selectively access the information stored on-site. U.S. Pat. No. 4,799,169 issued to Mims is directed to a gas well flow instrumentation apparatus including a computation unit and an interrogation unit. The computation unit measures parameters of gas flow at the well head and accumulates gas flow information over a plurality of different independent time intervals. The interrogation unit can be used to calibrate the computation unit and to make a permanent record of the information via on-board integral printer.
A low cost data logging device is disclosed in U.S. Pat. No. 4,414,633 to Churchill. Churchill's data logging device comprises a transducer means located in a gas supply line which provides an electrical signal having a pulse frequency representative of the magnitude of the parameter being measured A timing means is also provided to permit the measurement of the parameter at a predetermined time interval. A permanent record of the measurement of the parameter may be made on a printer device or the measurement may be stored in a memory. These devices are useful for the collection of data, particularly data relating to the flow of gas or fluids through a line but are limited to the passive collection of that data It is desirable to provide a single controller configurable to a plurality of applications and having a data logging function. A small hand held computer may be used by an operator to retrieve information from the controller concerning logged events at a particular site. Once collected, the resident controller memory may be cleared for the storage of new data. The hand held computer may be carried to the next site for similar data acquisition by the operator Upon completion, the operator may then carry the hand held computer back to a home base where the data retrieved from the various well sites may be downloaded to another computer having various data base or spread sheet programs to provide immediate production reports for each of the remote controllers.
The present invention contemplates a new and improved controller which overcomes all of the above problems referred and to above others and meets the above stated needs to provide a new gas and oil well controller which is readily adaptable to a plurality of well operational environments and uses with wells having a variety of operational characteristics and parameters, and which is easy to install, easy to operate, inexpensive to manufacture, provides improved well control and production, and which provides improved well head security.